The present invention relates to a photo-magnetic disk driving apparatus having therein an improved device for generating an external magnetic field perpendicular to a medium for recording or erasing information, in a photo-magnetic recording apparatus.
In the photo-magnetic recording apparatus wherein a magnetic field of a certain level is applied on a recording medium, such as a photo-magnetic disk, recording or erasing of information is made by causing the direction of residual magnetization on the recording medium to be the same as that of magnetization of a magnetic field applied concurrently through the method of applying laser beams on the recording medium and heating partially beyond a Curie point. There is needed an external magnetic field generating device with which the point in the vicinity of an optical spot formed on the medium is put in a certain magnetic field whose direction in recording is opposite to that in erasing. In the past, in order to change a direction of an external magnetic field to be applied on a recording medium for recording or erasing in a photo-magnetic recording apparatus, a method for switching a direction of an electric current running through a coil by the use of an electromagnet, or a method for rotating a permanent magnet mechanically or moving it in parallel has been used.
Namely, a direction of magnetization at a laser-applied portion is changed, for recording or erasing, by a magnetic field generated by energizing a coil (electromagnet). For recording, laser beams are applied on a recording medium by which a temperature at the laser-applied portion is raised, and at the same time, a bias magnetic field is applied by an external magnetic field generating device. For playing back, photo-magnetic effects of aforesaid recording portion are used.
FIGS. 7 (A) and 7 (B) show a conventional photo-magnetic disk driving apparatus in which a photo-magnetic disk is loaded. FIG. 7 (A) represents a top view, FIG. 7 (B) represents a sectional view taken on line at the center of the top view. FIG. 8 represents an exploded perspective view of the photo-magnetic disk driving apparatus and of the photo-magnetic disk.
In these figures, the numeral 1 is a photo-magnetic disk, 2 is a cartridge containing the disk, and 3 is a shutter (cover) for opening or closing the opening 2A on the cartridge 2. A hub portion of aforesaid photo-magnetic disk 1 can be mounted detachably on clamper 5 positioned on the top end of spindle motor shaft 4 of a driving apparatus in a photo-magnetic recording apparatus.
When either recording or erasing is made in aforesaid photo-magnetic recording apparatus, external magnetic field-generating device 6 in the apparatus is lowered so that it comes near the recording face of photo-magnetic disk 1. Aforesaid external magnetic field-generating device 6 is located so that it faces optical head 7 with the photomagnetic disk between them, and it is composed, in the access direction of optical head 7, of yoke 6A having a length to cover the scanning area of optical head 7 and exciting coil 6B wound around the yoke.
Aforesaid optical head (optical pick-up portion) 7 is composed of objective lens 7A, actuator portion 7B, laser diode portion 7C and photo-detector portion 7D, and it is mounted on carriage 12, which is capable of moving from side to side along two guide bars 11 placed in parallel on stationary base 10 of the photo-magnetic recording apparatus. The carriage 12 travels straight, being powered by thrust-generating device 13 composed of magnetic circuit 13A and driving coil 13B.
Next, FIGS. 9 (A) and 9 (B) show a cassette-loading mechanism in the vicinity of an external magnetic field-generating device in a conventional photo-magnetic disk driving apparatus, wherein FIG. 9 (A) represents a front view and FIG. 9 (B) represents a top view.
In these figures, the main structural members of the cassette loading mechanism are stationary base 10, movable base 20, cartridge-holder 21, DC motor M for loading, external magnetic field-generating device 6, movable base sliding mechanism (unillustrated) and an opening and closing mechanism (unillustrated) for shutter 3 of cartridge 2.
FIGS. 9 (A) and 9 (B) show how cartridge 2 is inserted. Under such conditions, movable base 20 can move back and forth in the direction of arrow A on stationary base 10 along the unillustrated movable base sliding mechanism.
On both sides of cartridge-holder 21, roller 22A and 22B are supported rotatably. These rollers 22A and 22B are in contact slidingly with slanted cam surfaces 20A and 20B of movable base 20, and are in pressure-contact, due to the tension force of coil spring 23 with movable base 20. Further, rollers 22B are engaged with elongated guide grooves 20C provided on both sides of movable base 20 and fixed on stationary base 10. Therefore, cartridge-holder 21 can move vertically against movable base 20.
When inserting cartridge 2 into cartridge-holder 21, cartridge 2 is to be inserted in the direction of arrow B to the stop position in cartridge-holder 21 through an opening thereon, as shown in FIG. 9 (A). During the course of insertion of cartridge 2, shutter 3 of cartridge 2 is moved by the unillustrated shutter opening/closing mechanism, and opening 2C of cartridge 2 is opened, thus a part of photo-magnetic disk 1 inside is exposed.
When cartridge 2 comes near the stop position that is the final step of cartridge insertion course, a front edge of cartridge 2 touches pin 26A located at the tip of L-shaped lever 26 in the locking mechanism, and rotates the lever 26 clockwise against the urging force of a spring. Due to the rotation of the lever 26, pin 26B provided on the other end of the lever 26 is disengaged from locking claw 20D on movable base 20. Thereby, movable base 20 moves in the direction of arrow C, being urged by pressure force of pin 24A positioned at the tip of activating arm 24 that is urged by coil spring 25 and thereby is rotatable round shaft 24B. When cartridge 2 moves, rollers 22A and 22B provided on cartridge-holder 21 slide down along the slanted cam surfaces 20A and 20B, and concurrently with that, roller 22B goes down along guide groove 20C and movable base 20 is moved down entirely by the urging force of coil spring 23. This downward movement causes cartridge 2 contained in cartridge-holder 21 to go down and the hub portion of photo-magnetic disk 1 inside cartridge 2 is engaged with and fixed to clamper 5 at the top end of spindle motor shaft 4 in the photo-magnetic recording apparatus.
When ejecting cartridge 2, a switch for ejecting cartridge is turned on, and then motor M operates and causes pin 27 provided on gear G4 to rotate counterclockwise through the gear train of G1, G2, G3 and G4. The pin 27 presses claw portion 20E provided on one end of movable base 20 to move the movable base 20 in the direction opposite to aforesaid C. Due to the reverse movement of movable base 20, cartridge-holder 21 causes movable base 20 to move upward through the action opposite to that made in the aforesaid movement of cartridge-holder 21 so that movable base 20 returns to its initial position, and at the same time, cartridge-holder 21 closes shutter 3 of cartridge 2 and moves cartridge 2 in the direction opposite to that of arrow B. Thus, cartridge 2 becomes possible to be taken out at the entrance.
FIG. 10 (A) is a top view showing how an external magnetic field-generating device is supported and FIG. 10 (B) is a sectional side view thereof. The external magnetic field-generating device is supported on supporting member 28 rotatably and is urged by a spring. One end of the supporting member 28 is supported rotatably on stand 29 fixed on stationary base 10, while the center portion of the supporting member is linked with cartridge-holder 21. FIG. 10 (C) is a sectional view of the portion in the vicinity of the external magnetic field-generating device wherein cartridge 2 is in its lowered position.
FIGS. 11 (A) to 11 (C) are longitudinal sectional views of the center portion taken from a front view of the photo-magnetic disk driving apparatus and FIG. 11 (A) shows a view wherein a cartridge is not loaded. Under such conditions, cartridge-holder 21, which is capable of moving vertically, is in its raised position and external magnetic field-generating device 6 is positioned to be higher than the top surface of the cartridge-holder 6.
FIG. 11 (B) is a sectional view showing the process of how cartridge 2 is loaded. In this process, the lower surface of external magnetic field-generating device 6 is positioned to be away from the upper edge of insertion path for cartridge 2 by the distance P.
FIG. 11 (C) shows a state wherein cartridge 2 has been loaded to its prescribed stop position When cartridge 2 is in its lowered position, external magnetic field-generating device 6 is in its prescribed position, which is in the vicinity of the obverse of photo-magnetic disk 1, through opening 21A of cartridge-holder 21, as well as through an opening of cartridge 2 and an opening of shutter 3.
In aforesaid photo-magnetic disk driving apparatus, the external magnetic field-generating device is required to be provided at a position higher than the upper stop position for the cartridge-holder that moves vertically. Therefore, it is necessary to prepare sufficient upper space, which makes it impossible to develop a small-sized driving apparatus. Further, when playing back and recording, the moving distance from the upper stop position to the lower set position to be close to the photo-magnetic disk is great, which causes problems of greater pressing force and impact force.